Embodiments of the invention generally pertain to systems and methods for processing signals and/or data sequences that correspond to signals for applications including data recording and data communication.
In particular, embodiments of the invention pertain to systems and methods for estimating the baseline wander of a signal, and for compensating for the baseline wander of the signal during detection of the signal.
Many data recording and data communication systems include processing stages for performing a variety of data processing and/or signal processing functions on a signal. These processing stages are often alternating-current (AC) coupled for reasons that may include practical circuit design or fundamental physics considerations. By way of example, AC coupling is sometimes used in digital circuitry to couple a first digital processing stage having a certain voltage level corresponding to a logical “high” to a second digital processing stage having a different voltage level corresponding to a logical “high” so that the two digital processing stages can be used in sequence to digitally process the signal.
When the signal includes low frequency components, such as direct current (DC) components, the AC-coupling can suppress or eliminate the low frequency components in the signal, which distorts the signal. The distortion of the signal can result in fluctuation of the signal's moving-average amplitude. As used herein, a signal's moving-average amplitude, also known as its DC component, is generally referred to as the signal's “baseline” or “baseline component,” and fluctuations of the baseline are generally referred to the signals “baseline wander.” Thus, the above-described distortions of the signal result in baseline wandering.
In addition to AC-coupling, there are other sources of baseline wander including other processing stages, communication channels, and/or storage channels that take on high pass filter (HPF) characteristics, which distort the signal by suppressing low frequencies thereby resulting in baseline wander.
To mitigate baseline wander, designers sometimes include specialized encoders. The encoders encode an input sequence of data such that when the encoded sequence of data is modulated into a signal, the signal will have a baseline that is low in magnitude. Thus, baseline wander does not have a significant impact on the overall signal.
However, these encoders and their associated decoders add complexity to transmitter and receiver structures, and even when such encoders are used they typically do not remove all of the signal's baseline component. Thus, it would be desirable to provide improved systems and methods that estimate baseline wanders in signals and compensate for the baseline wanders when detecting the signals. It is preferable that the methods have low latency, so that compensating for the baseline wander in the signal does not add significant delay to the detection of the signal. Furthermore, it is preferable that the signal is compensated for baseline wander as it is being detected, resulting in zero or near-zero latency.